1. Field of Invention
This invention relates to method and apparatus for performing environmental surveys and prospecting for contaminants in alluvial materials and bedrock formations. More particularly, the invention relates to a system for the use of drilling apparatus and associated equipment for effective and efficient environmentally related drilling through both soil and bedrock, including setting and pulling casing, to enable sampling and analyzing soil vapors, collecting soil and water samples, completing ground water monitoring wells, installing and testing air sparging and vacuum extraction remediation apparatus through both soil and bedrock and testing for successful remediation.
2. Description of the Prior Art
The invention comprises an effective, efficient, and economical system for drilling in soil and bedrock, dealing with temporary casing and for in-situ sampling, testing, detection and/or for preparation for remediation of soil, bedrock, and ground water contamination. The system provides for the in situ collection of soil vapor, for the collection of soil and bedrock samples from discrete intervals and for the collection of ground water samples. The system facilitates the construction of temporary or permanent ground water monitoring wells for collecting ground water samples and in-situ air permeability testing. The system affords multiple site characterization techniques for investigating and remediating contaminated soils and ground water.
At locations where soil, bedrock, and/or ground water contamination occurs, it is often desirable to collect soil vapor data to determine the extent of vapor phase contamination. A monitoring system to sample soil vapor has enhanced effectiveness, efficiency, and economy if the same apparatus can be used to collect soil samples, ground water samples and to complete ground water monitoring wells, as the situation may require. It would also be desirable to have the above apparatus capable of installing and testing remediation equipment, including temporary casing. The system would have even further general application if the drilling mechanism were capable of boring through bedrock and consolidated formations as well as through alluvial materials and unconsolidated formations, and could unclog bit perforations without pulling the bit. Prior to this invention, environmentally related drilling systems have not been offered to provide this effective and efficient combination of field data collection and well completion techniques through both soil and bedrock.
Prior and present art soil vapor surveying techniques use hand drilling and hydraulic drilling. The industry has stayed away from pneumatic drilling with its concomitant circulating air systems because of a general belief that such pneumatic drilling would distort the soil vapor data. The present inventors, faced with a daunting task of environmental surveying through bedrock, experimented nonetheless with pneumatic drilling and circulating air systems, notwithstanding the negative reception it receives in the art. The inventors learned that, unexpectedly, an air balance is apparently achieved downhole. Air pressure and venturi effects may cancel each other out at the probe tip. Pneumatic drilling, thus it was discovered, can be used for environmental prospecting and it does not impermissibly dilute or destroy the soil vapors sampled, the significance of the vapor analysis data or other soil or water data.
In contrast to prior art soil vapor sampling machines and techniques, the present invention, through the use of rotary percussion drilling equipment, preferably pneumatic, is not only able to sample through bedrock but is also able to efficiently and effectively provide a technique capable of water sampling as well as soil sampling, and capable of the installation of ground water monitoring wells in both alluvial materials and bedrock formations. The subject invention provides the synergistic advantage of performing multiple field investigative tasks both in alluvial and bedrock subsurface environments. By performing soil vapor surveys, collecting soil and/or ground water samples for laboratory analysis, and installing ground water monitoring wells and remediation equipment in both bedrock and alluvial materials, the system qualifies uniquely to offer a range of field services not currently found in the trade. Some specific advantages of the system's drilling apparatus and techniques, including preferred embodiments, are that it uses conventional rock bits which allow a rapid drilling rate in both alluvial and bedrock environments. Rapid downhole techniques have been developed for blowing out clogged perforations that occur when running rock bits in certain soft soil. Consequently, site characterization and the remediation of contaminated sites can be achieved at a rapid pace, allowing the system to provide more information to land owners for a lesser cost than the alternative of using a combination of prior systems. Furthermore, the drill cuttings (contaminated wastes) produced by the drilling apparatus and technique are of substantially less volume than that produced by many other drilling techniques, thereby reducing contaminated soil disposal costs. Because of the drilling procedure utilized, the apparatus provides a cleaner bore hole wall than that offered by other drilling techniques. A cleaner bore hole wall allows any remediation system installed to become effective more quickly. The apparatus and system of the present invention is further unique in the trade in that in addition to investigative techniques, it can be utilized to both install and test air sparging/vacuum extraction remediation systems. Once the remediation equipment is installed (sparge or vacuum point), the machine may be used to inject air into the sparge pipes and measure air pressure responses in the bore hole located at varying distances from the air injection point. This data can then be used to determine the effective air permeability of soils/bedrock for the efficient design of remediation systems, whether using air sparging/vacuum extraction independently or together. As cost control is becoming an increasingly important issue for environmental investigation and remediation, an apparatus and system that performs more efficiently and effectively both investigative and remediation tasks through a variety of subsurface environments is of enhanced value.
The invention further includes a method that is particularly adapted for testing water and soil during various phases of remediation and/or after remediation is deemed to be completed to confirm that contaminant concentrations have been reduced to levels within certain acceptable specifications. The prior art teaches the use of an hollow stem auger in such circumstances to drill test holes to determine if remediation is successful and complete. The auger drills to the water table to sample water and/or soil to confirm that the water or soil is clean. One benefit previously believed to adhere to the use of an auger was that the drilling itself was believed not to affect characteristics of the soil and water that needed to be tested. It was thought that pneumatic or hydraulic drilling would affect or destroy those characteristics, such as by using drilling fluids downhole as well as by using lubricants for the drill bit.
Several disadvantages of hollow stem auger drilling are obvious, namely, it is slow, inefficient and requires a large hole, approximately seven inches in diameter as opposed to two or three inches. But more recently discovered, for reasons presently unclear, the auger method also appears to lack its one perceived virtue, namely, not to affect important characteristics of the soil and/or water by the drilling process. Recent results from testing using prior art techniques after apparently successful remediation have appeared unrealistically negative. It is speculated that the cause may be that heat and pressure generated by the auger is vaporizing portions of the down-hole substances through pressure and friction. These vapors may migrate and contaminate adjacent soil and/or water.
Surprisingly, contrary to established expectations and the prevailing wisdom of the field, a rotary percussion drilling machine, preferably pneumatic, that circulates air or gas to remove the drill cuttings does not significantly appear to affect characteristics of the soil or water important to measure after remediation. Vaporizing of subsurface material is minimized using the rotary percussion drilling because the bit is cooled with circulating air or gas. Lubricants for the bit can be chosen that do not affect the results of the testing.
When testing subsequent to remediation, subsurface fluids, such as water, are not customarily lifted by vacuum pump. As there is no requirement to sample the soil and/or water while the drilling proceeds, a bore hole can be drilled directly to six inches or so below the water table, the drilling apparatus removed and the hole developed with temporary casing. Water is then lifted mechanically from the bottom of the hole, the casing pulled, and sample soil extracted from the hole, above or below the water table, using a device such as a split spoon sampler. The water and soil are subsequently tested for contaminants.
The present invention solves several difficulties that can be encountered when using a portable rotary percussion drilling machine for environmental surveying or prospecting. Perforations in the drill bit can become plugged when drilling through certain subsurface soils or materials, and difficulties can be encountered in certain subsurface formations in setting and removing temporary casing in a drilled borehole. The present invention includes method and apparatus for efficiently and effectively blowing out clogged perforations in the bit while drilling, and also includes adaptations to permit using the drilling machine itself to help set and remove casing.